In a mobile-type personal computer, a built-in semiconductor storage device with lower power consumption has been sought. For this purpose, a function to enter a low power consumption mode is provided to allow transition when there is no access from a host (i.e., at the time of idling) or when a request for transition to the low power consumption mode is issued from the host. In general, transition to a low power consumption mode accompanies a procedure of saving management information and operation information necessary for return in a non-volatile memory before turning off a power supply of a controller and a volatile memory. In a particular condition of use, however, a request for transition to the low power consumption mode may be issued from a host very frequently. In this case, if the management information and the operation information necessary for return are written in the non-volatile memory every time the request is issued, the number of times of writing to the non-volatile memory is increased. Accordingly, the non-volatile memory would be exhausted, leading to a failure of securing reliability of the non-volatile memory. Meanwhile, by writing the management information and the operation information necessary for return in the volatile memory to ensure reliability of the non-volatile memory, cancellation of a conduction of the volatile memory would be prohibited, to thereby minimize an effect of reducing power consumption.